Novartis AG is bolstering its radioligand arsenal with the takeout of Mariana Oncology Inc. for $1 billion up front and as much as $750 million in potential milestone payments. Watertown, Mass.-based Mariana has developed peptide-based radiopharmaceuticals targeting solid tumors. The company’s lead program, MC-339, is a radioligand approach to small-cell lung cancer, due to enter the clinic later this year.